1. Sulphuric Acid.— 3 grams, diluted with 10 c.c. of water, are treated
with 2 c.c. of cone, hydrochloric acid and a few drops of barium chloride
solution : no turbidity should be produced within an hour.
2. Hydrochloric Acid.— 2 grams, diluted as above, are treated with
silver nitrate : no opalcscence should result.
3. Nitric Acid. __ To 4-5 c.c. of the acid are added a little copper turn-
ings and about I c.c. of cone, sulphuric acid ; the liquid is then heated and
any evolution of red fumes observed.
4. Hydrofluosilicic Acid. — To 4-5 c.c. of the aeid is added saturated
potassium chloride solution : in presence of hydro tluosilieie. add, a white,
gelatinous precipitate is formed.
5. Arsenic, Heavy Metals, etc.— 5 grams of the add are diluted with
20 c.c. of water, the liquid heated and a current of hydrogen sulphide passed
through : a yellow (arsenic) or brown precipitate (heavy metal) may be
5 grams are diluted with 50 c.c. of water, rendered alkaline with
ammonia and treated separately with ammonium sulphide, ammonium
carbonate and ammonium phosphate for the detection of iron, lime and
6. Fixed Residue.— 10 grams are evaporated in a platinum dish.
7. Organic Matter. — Aeid containing this decolorises potassium
The pure acid should leave no woighablc fixed residue.
ro5 roB) or in
7 :i<33)- lt:
HaSiFo — i44'3
This occurs commercially in 7-10% solution (1) -•.
greater concentrations up to 20 or about 35% P :: ;
contain sulphuric acid and heavy metals as impurities.
1. Sulphuric Acid.- ....... -5 c.c., diluted with an equal volume of water,
and treated with strontium nitrate solution (free from barium), should, not
become turbid, even on standing.
2. Metals.— 5 c.c. .should leave no appreciable residue on evaporation
in a platinum dish. 5 c.c., diluted with as much water and a few drops
of hydrochloric acid, should remain unchanged by hydrogen sulphide, even
after being rendered alkaline with ammonia.
3. Quantitative Determination .--This is effected by precipitating
as potassium fluosilicate or by titration with N/2-alkali at the boiling point
in presence of phenolphthalein, or in the cold in presence of methyl orange,
and 25 c.c. of 22% calcium chloride solution. I c.c. N/2-alkali <•-•?. 0-012
A syrupy, odourless, colourless, highly acid liquid, soluble in all pro-
portions in water, alcohol or ether, but insoluble in benzene or chloroform.
The pure acid generally contains 75-80% of the acid (I) — i-2i~r23), the65% by weight of HF (D = 1-23-1-263)